1) Some server boards don't have PCIe x16 slot because a srver doesn't need someting better than a basic/integrated gaphic card.
2) Usually have one o more PCI-X slots.
3) ECC memory (i don't really know the difference)
4) Usually don't have a sound card integrated.
5) They have more memory slots.
6) Some boards support two or more CPU (most of them uses Xeon processors, but entry level boards uses core2)
7) Many of them are eATX, which don't fit in many regular cases
In most cases a server is not the way to go with video editing. Companies like Asus and Supermicro offer "Workstation motherboards". The main difference is that they have PCI-X slots (and/or 4x and 8x PCIe slots) for specialized cards, such as disk controllers and high end editing hardware. And Tyan has models for Xeon processors.